1. Field of the Invention
The present invention relates to a device for heat sealing and severing thermoplastic film materials, especially to make packages utilizing the film as wrapping material, and especially when the film is a heat shrinkable film. The heat sealing and severing device is most often used on continuous, horizontal packaging machines in which a single web of film material is formed into a tube while a succession of objects to be wrapped is fed into the tube being formed. The device of this invention is used to make a transverse seal in the tube and to sever the tube at the seal in such way that each severed end has a transverse seal.
2. Description of the Prior Art
Heat seal and cut-off devices for thermoplastic film material have generally been constructed such that the sealing and severing element must be activated and moved in a line longitudinally with the film material to provide adequate contact time to complete the seal. Moreover, such devices have usually been designed to yield fin seals rather than bead seals in final wrapped packages.
Heat seal and cut-off devices have also been made with counter-rotating knives and anvils wherein there have been used fixed clamping bars and anvil surfaces which have a fixed radius. Such devices cause packaging film used therewith to be scratched or torn by the clamping bars and the short contact time between knife and film requires slow operation for adequate sealing.